A faller child from an alternate timeline where Giovanni won by controlling Mewtwo (and Zeraora), leading him to take over Japan. The country, especially the Kanto region, quickly became a gang-run place, unsafe for anyone not directly supporting their cause. Shizuki's parents were killed due to being strong trainers that were outspoken against Team Rocket, leaving her to be an orphan in a place with no support. She mainly survives relying on herself and leeching off youth groups (mini-gangs), until one day, while in dire trouble, she suddenly falls through a wormhole into the prime dimension.
She's found by a young Alolan woman who was working in Kanto at the time, who was very shocked to find what appeared to be a war orphan. She initially turned Shizuki over to the authorities, but after checking up on the case and finding out she's a completely unregistered person with no family looking for her, chose to adopt her.
After Shizuki's health improves and her education is back on track, the two move back to Alola to give Shizuki a fresh start on life. Shizuki is happy to be away from a place that is associated with bad memories, and to be in such a peaceful place full of kind people. Naturally, she inserts herself into as many people's lives as possible to avoid dwelling on her own.
Mizumo (水萌) is an orphan from Kanto, who is sent to Alola with some others from her orphanage to "make a new life" in the so-called New World. Being a total orphan with an energetic and fast-learning personality, made her a prime candidate for this program. She mostly goes around making herself busy and sticking her nose in people's business, being a bit too young to have any exact ideas of what she should be doing. Becoming a jack-of-all-trades mixed with naïve bravery does make her a popular helper, though. Enjoys trying to figure out what people's problems are and fixing them, though this mostly results in irritation. It's definitely not a way for her to avoid working through her own issues.